Patient head support systems for securing the head of a patient during surgical or radiological procedures are known in the art. Such head support systems typically include a base unit that connects to a patient table, a skull clamp or headrest that holds a patient's head, and intervening structure for interconnecting the base unit to the skull clamp or headrest. These components, namely, the base unit, the intervening structure, and the skull clamp or headrest, adjust so the head of the patient may be secured in any one of a number of different positions, either for a particular radiological view or to facilitate access to a patient's head during a surgical procedure.
Typically, the base unit has two legs that connect to a table, a crossbar that extends between the two legs, and a base unit handle. The base unit handle has an elongated body that connects to the crossbar at a first end of the elongated body. The other end of the elongated body connects to an intervening member, such as a transition member or an adaptor, which in turn supports a skull clamp or headrest that holds the patient's head. These components, i.e. the skull clamp or headrest and the one or more intervening members, along with the base unit handle, enable operating room attendants to adjust the height, distance, and orientation of the skull clamp or headrest with respect to the end of the table, to hold the patient's head in a desired position.
For such head holding systems the intervening member, typically a transition member or an adaptor, has a cylindrically shaped post, or shaft, that is sized to be received within a complementary shaped bore at the second end of the elongated body of the base unit handle. The base unit handle has a lever that moves to and from the elongated body to contract and to expand, respectively, the diameter of the bore. With the lever moved to a closed position, adjacent the elongated body, the contracted diameter of the bore of the base unit handle rigidly holds the post and hence the intervening member. More specifically, once the intervening member, for example, a 6″ transition member, is installed, closing the lever of the base unit handle will, via cam action, exert a force to squeeze the bore tightly against the cylindrical post of the transition member. This creates frictional force to immobilize the base unit handle and the transition member. This frictional force must be sufficient to hold the system in a rigid fixed position, to stably support the patient. This closing of the lever of the base unit handle also closes or clamps the first end of the elongated body to the crossbar.
To function properly, i.e. to supply sufficient rigidity, the bore of the base unit handle and the post of the intervening member depend on very close tolerances. As a result, the surfaces typically used to achieve this lockable bore-on-post connection require a consistent surface finish, to provide smooth movement in the free state and to provide security when locked.
Also, the base unit handle can be damaged by the inadvertent moving of the locking lever into the closed position when the bore is empty. This can cause permanent distortion of the bore due to the compound leverage achieved via the closed lever. This vulnerability can perhaps be better understood with respect to the structure of the elongated body of the base unit handle. More specifically, a slot formed in the elongated body and in communication with the bore allows the elongated body to flex very slightly, so that the bore can constrict when the lever closes, as taught in U.S. Pat. No. 5,564,663. More specifically, the cam linkage of the lever is capable of exerting such a force on this bore structure that it can permanently bend the casting that defines the bore. Once the bore has been bent out of shape, it is highly possible that the post will no longer fit in the bore, at least not with the proper frictional fit.
For these reasons, with this type of head support system, the intervening member should always be connected to the base unit handle with the lever in the open position, such that the post of the intervening member is placed inside the bore and then the lever closed thereafter. Also, a caution warning is usually given to the users of such head support systems, to discourage them from closing the lever of the base unit handle when the bore is empty.
Also, when the lever moves from the locked to the unlocked position, it can accelerate rapidly if it is not being actively controlled by the user. If not controlled the lever will travel to its limit and stop abruptly. There are minor differences from one casting to another. Depending on the casting the lever stops when the linkage cannot move any further, or it stops when the corresponding cam rod strikes the casting. If the linkage stops because the cam rod is striking the casting, the repeated impact of the cam rod actually can push material into the bore.
When this occurs, a bulge of material may intrude into the bore, which can make it difficult or impossible to remove the intervening member. For this reason, in addition to the above described warning to close the lever only when the intervening member is inside the bore, it is also helpful to warn or to encourage such users to actively control the lever during opening, to avoid this striking of the casting by the cam rod. Unfortunately, such warnings are not a failsafe solution to these problems.
In addition to these issues, the outer surface of the cylindrical post of the transition member, when separated from the base unit handle, is susceptible to being marred by careless handling. If such marring occurs to the post, the locking function of the base unit handle can be rendered inoperable. In other words, the bore of the base unit handle and the post of the transitional member are in some respects very susceptible to mishandling by surgical attendants, and such mishandling can result in inoperability of the head support system.
To some extent these issues are complicated by the consideration that clinicians will want to be able to connect the intervening member to the base unit on either the right side or on the left side, depending on the circumstances, so that the intervening member can be removed from the base handle unit and switched around to face the other direction, when the opposite orientation is required. Clinicians are accustomed to this degree of flexibility in the surgical theatre, and any reduction in this capability would not be acceptable.
It is an object of the present invention, with respect to patient head support systems, to eliminate the potential for inadvertently damaging the portion of the base unit handle that forms or defines the bore.
It is another object of the present invention to assure consistency and repeatability in achieving an immobilizing force between the bore of a base unit handle and an intervening member of a patient head support system.
It is still another object of the present invention to assure a long-lasting, consistent and robust connection of the components of a head support system, without diminishing the degree of flexibility currently achieved by existing components.
It is still another object of the invention to preserve and to protect the structure and operability of a base handle unit, in a manner that relies less on operator instructions and warnings, and more on the structure itself.